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要旨:
Semiconducting half-Heusler compounds based on NiSn and CoSb have
attracted attention because of their good performance as thermoelectric
materials. Nanostructuring of the materials was experimentally
established through phase separation in (T1-xTx '')T(M1-yMy '') alloys
when mixing different transition metals (T, T', T '') or main group
elements (M, M'). The electric transport properties of such alloys
depend not only on their micro- or nanostructure but also on the
atomic-scale electronic structure. In the present work, the influence of
the band structure and density of states on the electronic transport and
thermoelectric properties is investigated in detail for the constituents
of phase-separated half-Heusler alloys. The electronic structure is
calculated using different theoretical schemes for ordered and
disordered materials. It is found that chemical disorder scattering
influences the electronic transport properties in all substituted
materials. Substitution in NiSn-based compounds leads to high
performance n-type materials but only moderate p-type thermoelectric
properties. The latter is caused by the influence of the valence band on
the conductivity. For CoSb-based compounds, it is found that Sb
substitution with Sn keeps the bands close to the Fermi energy intact.
The resulting substituted alloys are excellent p-type materials because
of the characteristic valence band structure in the A direction.
[GRAPHICS]
The figure shows the fcc crystal structure (C1(b)) of the halfHeusler
compounds (prototype: MgAgAs, cF12, F (43) over barm, 216). (C) 2015
WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
